Testing OpenSim (0.9.1, 0.9.1.1 dev) on the latest mono 6.6.0.161, it has been found good to go both for building and running OpenSim on Raspberry PI.
Mono version 6.6 can be found on the mono-project download page.
Having said that, both 0.9.1 and 0.9.1.1 dev has only been verified to successfully run with the SQLite database, as both versions seems to have an issue loading primitems with MySQL or PostgreSQL in grid mode, which can prevent the simulator from successfully starting and loading a region. The issue both exists for mono 6.4 and 6.6 (and possibly for older versions - not tested).
The issue does not exist in the OpenSim version based on the xmiropensim repository.
Mono version 6.6 can be found on the mono-project download page.
Having said that, both 0.9.1 and 0.9.1.1 dev has only been verified to successfully run with the SQLite database, as both versions seems to have an issue loading primitems with MySQL or PostgreSQL in grid mode, which can prevent the simulator from successfully starting and loading a region. The issue both exists for mono 6.4 and 6.6 (and possibly for older versions - not tested).
The issue does not exist in the OpenSim version based on the xmiropensim repository.